Tuesday, December 11, 2012

Transient Ischemic Dilatation

Transient Ischemic Dilatation (TID) is an important finding on myocardial perfusion SPECT in that it can be an indication of extensive severe coronary artery disease.  The reversible/transient nature of the dilatation corresponds to its ischemic nature, and TID has been associated with a greater risk of future cardiac events. In one study, TID was associated with proximal LAD or multivessel >90% stenosis. In another study a transient dilatation ratio of 1.12 was 60% sensitive and 95% specific for critical multivessel CAD. Despite this, however, these findings are associated with a defect in the myocardial perfusion with stress; it is unclear how severe CAD really is in a patient with TID and no abnormality in myocardial perfusion.

Myocardial SPECT Lexiscan (40 mCi of Tc-99m-MIBI). There is a small, fixed apicoseptal perfusion defect as well as transient ischemic dilatation with stress. The green arrows point to representative pairs of stress/rest images (stress on top, rest on bottom), demonstrating an increase in the size of the left ventricle with stress (ratio 1.34).

One explanation for TID suggests that the apparent "dilatation" of the ventricle may be a result of subendocardial ischemia.  Other think that it may be a combination of this effect and true ventricular dilatation.

Myocardial SPECT Lexiscan (40 mCi of Tc-99m-MIBI) with gated SPECT analysis on both resting and post stress images. There is a small, mild anteroapical perfusion defect which is fully reversible. There is also transient ischemic dilatation (ratio 1.28).

Avoidance of false postive TID on SPECT is subject to good technique.  Motion artifacts, poor slice selection for comparison, and differences in administered radionuclide can cause artifactual TID.

1. Abidov A, Berman DS. "Transient ischemic dilation associated with poststress myocardial stunning of the left ventricle in vasodilator stress myocardial perfusion SPECT: True marker of severe ischemia?" Journal of Nuclear Cardiology. Volume 12, Number 3;258-60
2. McLaughlin MG, Danias PG. "Transient ischemic dilation: a powerful diagnostic and prognostic finding of stress myocardial perfusion imaging." Journal of Nuclear Cardiology Volume 9, Number 6;663-7